Laser beam projection apparatuses, such as, for example, point lasers, line lasers or in particular rotation lasers, are used in particular in construction or interior finishing, for example for vertically marking walls. A rotation laser marks a reference plane by means of its rotating laser beam. In this case, the laser beam itself can be emitted for example in a punctiform, linear or fan-shaped fashion. The laser light can be generated as continuous light or in a pulsed fashion. What is important here is that the laser beam is emitted with plane trueness, in particular horizontal trueness, that is to say that it remains exactly in the envisaged plane, in order to be able to preclude incorrect markings. In order to ensure this, conventional lasers of this type are generally equipped with a beam self-leveling functionality. A first adjustment of the horizontal trueness and calibration of the beam self-leveling functionality are typically carried out by the manufacturer prior to delivery of the laser.
At regular intervals or as required, it is necessary to test and recalibrate the plane trueness and/or horizontal trueness of the laser and the beam self-leveling functionality thereof and, if appropriate, to readjust the laser because the adjustment of the laser can change as a result of various external influences, such as, for example, temperature and moisture fluctuations, mechanical shocks, vibrations, etc.
For fulfilling this task, laser beam horizontal trueness testing devices are known and described in the prior art. These known devices usually comprise, as basic components, a telescope and an position sensitive detector for capturing the laser beam of the laser beam projection apparatus and determining out of the impinging position of the laser beam on the detector, if a deviation of an ideal orientation of the laser beam particularly with regard to its horizontality exists which makes a readjustment necessary. For example, such a laser beam horizontal trueness testing device is disclosed in EP 2741049 of May 12, 2012 by the same applicant.
As such a laser beam horizontal trueness testing device is also subject to said external influences, its precision might also diminish, e.g. after special events like shocks or temperature cycling due to a transport of the device. This might have the effect that the assumed point of true horizontality (level point) as defined by the current calibration parameters is not the real point of true horizontality. Therefore, verification of the calibration or to say a new calibration of the testing device itself can be necessary. For fulfilling this task, regular laser beam projection apparatuses are not suitable even if as accurate as specified and not maladjusted. This is, among other reasons, caused by the precision grade of these apparatuses which is not set up/designed to fulfill such a task, due e.g. errors introduced by the ball bearings of a rotational laser.
In contrast, it is possible to (re-)calibrate a laser beam horizontal trueness testing device using a total station, which is capable of providing a laser beam with the required precision.
However, it has to be assured that the total station itself has not been subject to external influences which have deteriorated this complex instrument. Further disadvantages are the significant costs of a total station or of a similar device and their complexity that necessitates a specialized skilled person for handling.